In recent years, tungsten having heat resistance and low resistance characteristics is widely used as a wiring material and an electrode material in the semiconductor manufacturing art. A tungsten film is typically formed by a sputtering method. In the sputtering film formation of the tungsten film, argon ions produced by plasma discharge are collided with a tungsten target to knock tungsten fine particles out from a surface of the target and to deposit the tungsten fine particles on a substrate disposed facing to the target. At this time, it is known that there is a great problem in the process that particles produced from the surface of the target attach on the substrate to decrease properties of the film. Accordingly, a tungsten target having fine and uniform crystal grains and a high relative density is necessary for stably forming a high quality tungsten film.
For example, Patent Document 1 describes a method of producing a tungsten sputtering target where a small amount of molybdenum is added to tungsten powder in order to prevent particle generation. It is described that the method can provide a target having a relative density of 95% or more and an average particle diameter of 10 μm to 300 μm.
Patent Document 2 describes a method of producing a sputtering target by loading tungsten powder into a metal capsule, pressing the powder at normal temperature, capsuling under vacuum, and then hot isostatic pressing (HIP) the capsule. It is described that the method can provide a target having an average crystalline particle diameter of 20 μm to 100 μm, a relative density of 99% or more, and an oxygen content of 10 ppm to 15 ppm.    Patent Document 1: Japanese Patent Application Laid-open No. 2001-295036    Patent Document 2: Japanese Patent Application Laid-open No. 2003-193225